Ion-specific membrane

ABSTRACT

AN ION-SPECIFIC MEMBRANE INCLUDES A HYDROPHOBIC ELASTOMERIC POLYMER WITH A DIELECTRIC CONSTANT OF 4 TO 13, AND AN ION-SPECIFIC CARRIER. THE HYDROPHOBIC ELASTOMERIC POLYMER IS PREFERABLY AN ORGANOPOLYSILOXANE POLYCARBONATE   BLOCK COPOLYMER. THE ION-SPECIFIC CARRIERS INCLUDE H+ AND K+ ION CARRIERS.

July 3, 1973 J, BROWN, JR, ET AL 3,743,588

ION-SPECIFIC MEMBRANE Filed Oct. 18, 1971 //V VE/V TOR$-' JOHN E BROWN, Jn; GEORGE M. J .SLUSARCZUK; OLIVER H. LQBLA/VC, Jr:

THE IR ATTORNEY United States Patent Oflice 3,743,588 Patented July 3, 1973 3,743,588 ION-SPECIFIC MEMBRANE John F. Brown, Jr., George M. J. Slusarczuk, and Oliver H. Le Blanc, Jr., Schenectady, N.Y., assignors to General Electric Company Filed Oct. 18, 1971, Ser. No. 190,344 Int. Cl. G01n 27/46 US. Cl. 204-195 M 4 Claims ABSTRACT OF THE DISCLOSURE An ion-specific membrane includes a hydrophobic elastomeric polymer with a dielectric constant of 4 to 13, and an ion-specific carrier. The hydrophobic elastomeric polymer is preferably an organopolysiloxane polycarbonate block copolymer. The ion-specific carriers include H+ and K+ ion carriers.

This invention relates to ion-specific membranes and, more particularly, to such ion-specific membranes comprising a hydrophobic elastomeric polymer and an ionspecific carrier.

Such ion-specific membranes are employed to measure specific ion responses. These membranes can be used in various types of sensors.

Ion-specific sensors are known in the prior art for measuring the hydrogen ion activity or pH of'a sample or for measuring the potassium ion or other ion activities of a sample. An example of such a sensor is a-pH sensor which employs a hydrogen ion-specific electrode, such as a glass electrode, and a reference electrode immersed in a solution, whereby the potential difference between the two electrodes is a function of the concentration of the hydro gen ion in the solution. The reference electrode contains a salt solution. Electrical connection between the salt solution and the sample solution is made generally by a liquid contact through an aperture referred to as a liquid junction.

Organopolysiloxane polycarbonate block copolymers, which are preferred in our present invention as hydrophobic elastomeric polymers, are described and claimed in US. Letters Patent 3,419,634 issued Dec. 31, 1968 and assigned to the same assignee as the present appli-' cation.

Our present invention is directed to an improved ionspecific membrane which is suitable for biomedical, environmental control and other applications.

In accordance'with one aspect of our invention, an ionspecific membrane has a hydrophobic elastomeric polymer with a dielectric constant of from 4 to 13, and an ion specific carrier.

These and various other objects, features and advantages of the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

The single figure is a sectional view of a hydrogen ion-specific sensing electrode employing an ion-specific membrane made in accordance with our invention.

In the single figure of the drawing there is shown generally at an ion-specific electrode employing an ionspecific membrane made in accordance with our invention. A tube 11 of non-ion-selective material, such as glass has a disc 12 of ion-specific membrane sealed to one open end of glass tube 11 by a room temperature sealant 13 holding the edges of disc 12 against the exterior surface of tube 11. A silver wire 14' is positioned partially within tube 11 and extends outwardly from tube 11. Silver wire 14 has a portion of silver wire 15 and a portion 16 with silver chloride thereon.

We found thatwe could form an improved ion-specific membrane, which is useful for sensing a specific ion,

from an elastomeric polymer with a dielectric constant of from 4 to 13, and an ion specific carrier. Suitable elastomeric polymers with a dielectric constant of from 4 to 13 include polyurethanes, chloroprene polymers, vinylidene" fluoride-hexafluoropropylene polymers, and organopolysiloxane polycarbonate block copolymers with a dielectric constant of from 4 to 13. Such block copolymers are described and claimed in the above-identified U.S. Letters Patent 3,419,634. For example, suitable block copolymers with a dielectric constant of from 4 to 13 include phenoxysilicon linked cyanoethyl-methyl siloxane/ bisphenol-A copolymer, siloxane-carbamate/PBA-carbonate copolymer with diisocyanatosiloxane, siloxane-carbamate/BPA-carbonate copolymer with a ratio of SiMe /SiMeEtCN=3.3,

siloxane-carbamate/EPA-carbonate copolymer with a ratio of SiMe /SiMeEtCN=2.4, siloxane-carbamate/ PEA-carbonate copolymer with a ratio of SiMe /SiMeEtCN=0.13,

and siloxaue-carbamate/BPA-carbonate copolymer with a ratio of SiMe /SiMe(EtCN)=13.

Suitable ion-specific carriers include H+ ion carriers that are hydrophobic, lipophilic uncouplers, and include K+ ion carriers. Suitable uncouplers include p-dodecyldinitrophenol, p-octadecyldinitrophenol, p-octadecyloxyphenylhydrazone mesoxalonitrile, and p-octadecyloxy-mchloro-phenylhydrazone mesoxalonitrile. H+ ion carriers that are hydrophobic lipophilic uncouplers are based upon compounds belonging to a class of substances known to uncouple oxidative phosphorylation in mitochondria and chloroplasts, and are therefore called uncouplers. Our carriers are such uncouplers which have been rendered hydrophobic and lipophilic by the addition of long alkyl hydrocarbon chains at appropriate places on the molecules. The carriers may be employed in the form of the simple acid or in various admixtures with hydrophobic, lipophilic salts of the acid such as tetraheptyl ammonium salts. Alternatively, the salt forming ion may be structurally incorporated into the polymer to completely prevent its transfer to the aqueous phase. Alternatively neutral hydrophobic, lipophilic salts such as tetraphenyl ammonium-tetraphenyl borate may be added to the polymer. One of the purposes of adding the salt forming species is to increase the conductivity of the membrane and thereby reduce interferences from electrical noise.

The following preparations were employed to produce organopolysiloxane polycarbonate block copolymers for use in preparing the membranes of our invention.

(1) Phenoxysilicon linked cyanoethyl-methyl siloxane/ bisphenol-A copolymer.-A mixture of 15.7 g. of pentamethylcyanoethylcyclotrisiloxane (60 mmoles) and 1.3 g. of dimethyldichlorosilane (10 mmoles) and 20 mg. of ferric trichloride hexahydrate was stirred overnight under anhydrous conditions. An exothermic reaction was ob-- served during the first minutes, accompanied by a strong viscosity increase; the viscosity dropped during later stages of the reaction. The resulting a,w-dichloropolysiloxane was 'diluted with 10 cc. of anhydrous methylene chloride and added dropwise with stirring under anhydrous conditions to a solution of 6.85 g. of bisphenol-A (30 mmoles) and 7.8 cc. of dry pyridine in 60 cc. of methylene chloride. The mixture was stirred for about 30 minutes after completion of the addition; phosgene was then slowly passed into the solution until the viscosity rose sharply indicating the end of the reaction. The polymer solution was then washed twice with 10% hydrochloric acid and subsequently with water to neutrality. The product was recovered by precipitation into methanol. A yield of 17.2 g. was obtained, 70% of the theory. The NMR the copolymer.

Analysis.C50.8, H6.8, N--3.2, Si-22.4. In-

( 5 Siloxane carbamate/BPA carbonate copolymer,

SiMe /SiMeEtCN=0.13.-A solution of 22.4 g. of

siloxane fluid prepared from 290 mmoles of methylcyanoethylsiloxane cyclic and 20 mmoles of bisaminobutyldisiloxane was reacted with 6.1 g. of BPA-bischlorocart i i viscosity; 59 d1 bonate and 1.91 g. of pyridine, and subsequently with 3.9 (2) Siloxane-carbamatelBPA carbonate copolymer g. of BPA, 5.8 g. of pyridine and phosgene, as described with diisocyanatosiloxane.-A mixture of 44.5 g. of octa in Example 3. The polymer was recovered by addition to methylcyclotetrasiloxane, 22.5 g. of cyanoethylmethylmethanol; a yield of 19.5 g. of light-tan-colored, tough cyclosiloxane (mixture of trito hexasiloxane) and 5.4 g. rubber was obtained. of 1,3-bis(4-aminobutyl)tetramethyldisiloxane was heated (6) Siloxane carbamate/BPA carbonate copolymer, with about 20 mg. of solid sodium hydroxide under dry SiMe /SiMe(EtCN)=13.--An aminobutyl end-stopped nitrogen at 170 overnight. A solution of 14 g. of the resiloxane fluid was prepared by heating 29.5 g. of octasulting homogeneous fluid is about 60 cc. of dry toluene methylcyclotetrasiloxane (0.4 mole), 4.0 g. of cyanoethylwas saturated with phosgene and then refluxed until all methylcyclosiloxane (0.035 mole), and 5.4 g. of 1,3-bis excess phosgene and hydrogen chloride were removed (4-aminobutyl)tetramethyldisiloxane (0.02 mole) with (about 5 hours). Toluene was stripped off, the residue disabout 10 mg. of sodium hydroxide at 190 C. for 15 hours solved in about cc. of dry methylene chloride and a under nitrogen. This fluid was reacted first with 3.24 g. solution of 5 g. of bisphenol-A and 6 cc. of dry pyridine of pyridine (0.041 mole) and 10.6 g. of BPA-bischloroin 50 cc. of methylene chloride was added at once with 20 carbonate (0.03 mole) in 80 cc. methylene chloride. BPA, stirring. Phosgene was now bubbled slowly into the stirred 6.84 g. (0.03 mole), and 10.0 g. of pyridine were then solution which toward the end of the reaction turned added and the resulting mixture was phosgenated as demoderately viscous. The workup and recovery of the prodscribed before. The polymer product was isolated and not were carried out as described in the previous example. purified as in earlier examples. A yield of 42 g. of a color- A yield of 8 g.of polymer was obtained which could be less, tough rubber was obtained. cast into a clear rubbery film from chloroform solution. Composition, physical properties, and analytical data (3) Siloxane-carbamate/BPA carbonate copolymer, for the above copolymers 2-6 are set forth below in SiMe /SiMeEtCN=3.3.-A mixture of 25 g. of octameth- Table I.

TABLE I $51515 Medl/ii eibi dmt iliilfi ififiit Dielectric Intrinsic siloxane Calculated Found constant viscosity in 00- Yield, Startin Starting N0. 7 dl./g. polymer percent Polymer materia Polymer material C H N Si 0 H N Si 6 4 2:e.4 0. 92 60 71 13 12 4. 3 49.2 7.2 1.8 23.8 49.6 7.5 1.6 22.2 5 5:2.5 1.13 63 61 3.3 5.0 2.6 3 50.0 7.0 4.3 22.7 49.8 7.2 3.8 21.4 6 15:.6 0.78 63 65 2.4 3.0 2.75 a 50.0 7.0 5.9 21.0 50.5 7.1 4.3 20.7 12i1 0.79 62 77 0.13 0.14 3.5 3 55.1 6.5 3.3 16.3 53.6 6.4 8.2 16.5 5. 22:1 0.3 52 42 2.2 3.2 9.3 5.7 53.5 6.4 3.7 18.7 54.9 6.6 3.2 17.0 In 0H01.,25. Twice-precipitated product. Prepared with diisocyanato siloxane II. ylcyclotetrasiloxane (340 mmoles), 8.5 g. of cyanoethyl- The following preparations were employed to produce methylcyclosiloxane (mixture of trito hexasiloxane; 75 H+ ion carriers that are hydrophobic, lipophilic uncoummoles) and 5.4 g. of 1,3-bis(4-aminobutyl)-tetramethplers for use in the specific membranes of the present inyldisiloxane (2O mmoles) was heated at 190 with about vention. The analysis of each uncoupler is set forth. 10 mg. of sodium hydroxide under nitrogen for 15 hours. 45 (I) p-Dodecyldinitrophenol (I).To a mixture of 25 A solution of 20.5 g. of the resulting homogeneous fluid ml. of 70% nitric acid, 35 ml. glacial acetic acid, and (10.5 mmoles) and 1.74 g. of pyridine (22 mmoles) in mi. acetic anhydride was added, at C. and with about 20 cc. of methylene chloride (dried with phosstirring, 26.2 g. (0.1 mole) of p-dodecylphenol dissolved phorus pentoxide) was added over a period of 30 minutes in ml. glacial acetic acid. The cold reaction mixture to the stirred solution of 5.6 g. of bisphenol-A-bischlorowas allowed to warm up overnight. carbonate (15.9 mmoles) in 20 cc. of dry methylene The solvents were evaporated in vacuo, and the residue chloride. Stirring was continued for another 30 minutes, dissolved in benzene and washed with water. Addition of then 3.6 g. of bisphenol-A (15.8 mmoles) and 5.3 g. of hexane caused a precipitate which was filtered off and pyridine (67 mmoles) was added and a slow stream of discarded. The solution was chromatographed on silica phosgene was bubbled into the stirred solution until a gel using z ne in hexane as eluant. The dinitrosharp rise in the viscosity indicated the end of the reacphenol was obtained as a viscous oil upon evaporation of tion. About 10 cc. of methanol was quickly added in the solvent. I order to quench the reaction and prevent gel formation. y for C18H28N2O5 (percent): C61.3, The solution was diluted with about two times the volume H8.0, N7.9. Found (percent): C-62.5, H7.4, N of chloroform and washed three times with water. The 7.9. p product was recovered by addition to methanol. A yield P octodecyloxyphenylhydfalone mesoxalonitrile of 23 g. was obtained. 7 (II).--3.6 g. (0.01 mole) of p-octodecyloxaniline was dis- (4) Siloxane carbamate/BPA carbonate copolymer, Solved in 250 dimethylformamide and SiMe /SiMeEtCN=2.4.As describedinthe previous exml. (0021111018) Of concentrated HCl was added with ample, an amine-end stopped siloxane fluid was prepared stirring. The mixture. was cooled to 3 C., and 0.7 g. from 22.4 g. of dimethylsiloxane cyclic (300 mmoles), (091111016) of Sodium nitrite, dissolved ina Sma mount 11.3 .g. methylcyanoethylsiloxane cyclic (100 mmoles), of Was added p y P- Stirring nued for and 5.4 g. of bisaminobutyldisiloxane (20 mmoles). As two hours, then a Solution of 8- mole) 111810110- in Example 4, a portion of the products, -19.4 g., was nitrile and 1 ml. triethylamine in 25 ml. DMF was added. reacted with 5.3 g. of BPA-bischlorocarbonate and 1.65 The ture Was left standing overnight. f idi d bs tl i h 3,4 of E A, 5 The mixture was acidified with HCl, warmed to dissolve g. of pyridine and hosgene, The reaction product was the precipitate, and left to cool in ice. Filtration afforded precipitated by addition to methanol containing about 4.0 g. 1%) of the product, a yellow solid. It was puri- 20% of water. A yield of 19.1 g. of a tough, colorless fied by recrystallization from methanol (M.P. 114 to rubber was obtained. 115 C.).

Analysis.-Calc. for C H NO (percent): C--73.9, H-9.7, N12.8. Found (percent) C74.7, H--9.8, N- 12.5.

used to measure zero-current potentials. The H+ ion response of various membranes are set forth below in Table II.

TABLE II Example Thickness Resistance I Response Sensitivity number Polymer Carrier (mm.) (ohm) time (see.) (mv./pH)

6 1% III. 0.21 4X10 5 30-60 58 4 1% III plus 1% H111 0. l8 2X10 ((30 59 B Area of each electrode approximately 0.7 cm. Resistance base films: 10 -10 12. b TPA-TPB tetraphenylarsonium+ tetraphenylboratv. HIII=salt of III with tetraheptyl ammomum (HI) p Octadecyloxy-m-chlorophenylhydrazone mesoxalonitrile (III).--To 8.6 g. (0.02 mole) of 3-chloro-4- octadecyloxyaniline hydrochloride suspended in 250 m1. DMF was added 2.3 ml. (0.02 mole) concentrated HCl, and the mixture was cooled to 3 C. With stirring 1.4 g. (0.02 mole) of NaNO dissolved in DMF was added. Stirring was continued for an hour, then 1.4 g. (0.02 mole) of malononitrile dissolved in 10 ml. DMF was added. After 10 minutes of further stirring 6 ml. of trimethylamine was added. The mixture was allowed to warm up overnight.

The reaction mixture was acidified with HCl, the resulting precipitate was filtered, washed with water, and recrystallized from methanol. Yellow needles, M.P. 105.5 to 106 C.

Analysis.--Calc. for C H CINO (percent): C-68.5, H8.74, (El-7.49, N--11.84. Found (percent) C68.4, H--8.4, C1-7.8, N11.8.

Examples of ion-specific membranes made in accordance with our invention are as follows:

EXAMPLES 1-9 Ion-specific membranes 1-9, which are Examples 1-9, were prepared from the above block copolymers and hydrophobic, lipophilic uncouplers by casting a film of the composition on a glass plate from a methylene chloride solution of the polymer and the compound. A circular portion of the composition was punched out and joined to the end of a glass tube having an internal diameter of about 1 centimeter with a silicone seal. The tube was filled with an aqueous chloride solution of 0.1 M potassium chloride buffered at pH 7, and a chlorided silver wire inserted as the internal electrode. This assembly was inserted in the solution to be measured along with a fiber-junction saturated calomel reference electrode (S.C.E.).

The potential difierence between the central electrode and the S.C.E. reference was displayed on a recorder after voltage amplification. The variable input resistance to the electrometer shunted the electrodes. Membrane resistance was estimated by measuring the decrease in displayed potential as the shunt resistance was decreased. A shunted resistance of at least two powers of 10 higher EXAMPLE 10 A membrane, which is Example 10, was prepared in the manner set forth above in Examples 1-9 but was not made with a hydrophobic elastomeric polymer with a dielectric constant of from 4 to 13 in accordance with our invention. An organopolysiloxane polycarbonate block copolymer was selected which had a dielectric constant of 2.9, was hydrophobic and elastomeric. Hydrophobic, lipophilic uncoupler No. III from the above uncoupler preparation was employed. However, this membrane, when assembled and tested as described above inExamples 1-9 exhibited a resistance of l 10 ohms and gave no response thereby showing its unsuitability as an ionspecific membrane.

While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such as may be embraced within the following claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An ion-specific membrane comprising a hydrophobic elastomer-polymer with a dielectric constant of from 4 to 13, and a H+ ion carrier which is an uncoupler known to uncouple oxidative phosphorylation in mitochondria and chloroplasts, said uncoupler being rendered hydrophobic and lipophilic.

2. An ion-specific membrane as in claim 1, in which the hydrophobic, lipophilic uncoupler is p-dodecyldinitrophenol.

3. An ion-specific membrane as in claim 1, in which the hydrophobic, lipophilic uncoupler is p-octadecyloxyphenylhydrazone mesoxalonitrile.

4. An ion-specific membrane as in claim 1, in which the hydrophobic, lipophilic uncoupler is p-octadecyloxym-chloro-phenylhydrazone 'mesoxalonitrile.

References Cited UNITED STATES PATENTS 3,562,129 2/1971 Simon 204-- M 3,419,634 12/1968 Vaughn 260-824 R TA-HSUNG TUNG, Primary Examiner US. Cl. X.R. 

